1. Field of the Invention
The present invention relates to an internal fixation device for treating scoliosis, and particularly, to a spontaneous-extending and anti-rotation scoliosis correcting system.
2. Description of the Relevant Art
Many adolescents seriously suffering from scoliosis need surgical corrections. Currently, pedicle screw-rod systems are often used in the surgical treatment. These existing fixing technologies have the following deficiencies and disadvantages.
1. For most pedicle screw-rod systems, after the scoliosis is corrected and fixed, the shape and length of the pedicle screw-rod systems cannot be adjusted. Although the scoliosis is effectively corrected, the restriction of the fixed segment, imposed by the internal fixation of the pedicle screw-rod system, leads to an arrest of growth of the spine. Since most patients being treated for scoliosis are adolescents, and their spines continuously grow, a crankshaft phenomenon occurs in which the growth of the spines near the fixed segment is distorted and deformed, and the patients' growth is seriously impacted. If the pedicle screw-rod system is removed early, the scoliosis may reappear. So it is clinically desired that a pedicle screw-rod internal fixing system should be able to spontaneously extend along with the growth of the spine.
2. Chinese patent No. 200510086711.6 discloses a extending rod system, wherein the extending rod is an integral structure slidably connected to a plurality of pedicle screws. In this system, the pedicle screw and the correcting rod are relatively slidable rather than being locked with each other, thus the spine growth is not restricted by the extending rod. Although this system can correct the lateral and angular deformities, the pedicle screw can rotate by taking the correcting rod as an axial, since the pedicle screw and the correcting rod are not locked with each other, thus the stability of the action achieved by the pedicle screw-rod system on the spine is greatly influenced, and a worse correction effect is achieved than with other pedicle screw-rod system. Particularly, the rotated vertebrae cannot be fixed, and it is ineffective to prevent the rotation deformity.
3. The prior art also proposes a growing valve system (e.g., ISOLA fixing device) that is designed to achieve both growth extension and anti-rotation. This system employs a structure similar to the traditional pedicle screw-rod system, wherein the correcting rod and the pedicle screw are locked with each other, and the correcting rod is added with a manually extendible growing valve. The design is the most advanced scoliosis correcting system at present. The design has a good anti-rotation effect, i.e., it realizes the scoliosis correction function of the common pedicle screw-rod system with a rotation stability, and partially meets the requirement of extending the internal fixing system along with the growth. However, the design still has the following serious deficiencies, which significantly influence the treatment effect and cause great pain to the patients.
a. Since manually extension is needed, the patient will need to undergo surgery every half year to expose the rod fixed on the spine, loosen the fixing screws of the growing valve, and adjust the internal fixing length. For example, with respect to the conventional ISOLA device, the surgical incision will need to be more than 25 cm to expose the internal fixing adjustment portion fixed on the spine. These procedures will result in additional damages to the patient both physiologically and financially. Furthermore, it is increases the chance of complications such as infection. Since many patients will not accept the frequent surgery, the growing valve cannot be adjusted in time, and the spine growth is influenced. It can be seen that the frequent surgical adjustment is a major deficiency for this technology.
b. The growing valve must be long enough to ensure an effective extension distance. In order to place the growing valve, the pedicle screws are fixed in an interval of multiple vertebrae. But the span increases with the interval, and the correction effect becomes poorer. In addition, large stresses may be caused at the upper and lower pedicle screws of the growing valve. This causes the screws or rods are to be easily fractured.
c. The normal spine continuously grows and requires the internal fixation to gradually extend rather than periodically extending. Thus the traditional growing valve system does not meet the physiological requirement of the spine growth. Furthermore, the single adjustment range at each time is very limited, thereby requiring frequent adjustment.
d. An extra-long linear growing valve may influence the spine shape, and may cause a “flat back” deformity of some spines.
In order to improve the system, Chinese patent No. 200510011913.4 modifies the growing valve system by adding a rack and a drive gear. Those devices may be reached via a small incision, and the whole correcting rod may be extended by rotating the drive gear. This method shortens the surgical incision and reduces the damage during the surgeries, but still cannot avoid the need for surgery every half year. Meanwhile, the drive gear, etc. has large gaps. Connective tissues may grow into those gaps, which could increase the risk of mechanical structure failure and surgery. In conclusion, there is a definite unmet clinical need to provide an internal fixing system capable of: correcting scoliosis and preventing rotation; is naturally extendible along with the growth of the spine without any surgery; is short-segment fixable; and is multi-segment extendible without influencing the local spine shape.